Hinkis suspects that Google has changed its search algorithm to
favour actual brands and company web sites over the Wikipedia
entries that are about them:

Wikipedia has long since been a huge competitor for brands in
terms of website traffic. SEO’s aren’t crazy about it, because it
takes a huge chunk of our traffic.

To be fair, there is no evidence that Wikipedia's traffic
loss is due to Google. We don't know how accurate SW's traffic
sample is. And traffic goes through seasonal and news-cycle
driven trends, and any of these could be affecting the site.

However, what Wikipedia taketh from other sites' traffic,
Wikipedia also giveth: The site is so massive that it also drives
a fair amount of traffic onward to other sites. But the less
traffic Wikipedia gets, the less it can give.

Business Insider asked Google for comment but we have not heard
back yet, so let's speculate.

One of the major trends happening at Google is the company's
preference for inserting its own content above the content of
other non-Google web sites, even when those sites may be better
resources than Google itself. Google's goal here is to give
people the best answer as quickly as possible.

Here is an example. If you're trying to remember who won the
World Cup last year, you might get this Google result:

Google

If you click on that down-arrow that Google provides for the
"roster and overview," you get a capsule on the German team.
That might be all you need, and Google believes this is so useful
it might save you a click.

The problem is that a few months ago that click might have gone
to Wikipedia. And in fact the info in the Google box is drawn
from Wikipedia. So on the one hand, this is good for Wikipedia
(its info is featured prominently and the box does give Wikipedia
a link). But on the other, Wikipedia thrives on clicks and this
box is designed to save you from actually clicking through if you
only need the bare bones info.